Firstly, when ordering from overseas (read robot kingdom :P) if the value of the order gets over a certain value, does the shipping become more expensive, or does this not affect the price at all.
I think it's mostly calculated by weight. This is Japanese but it's a pretty good guide. Yen on the side, weight below.



Secondly, if i preorder something within my original order will they ship the preorder item later or will they wait till the preorder item is in before shipping out the whole package?
I would think that if you ordered it all at the same time it would ship together. I ordered a bunch of BTs including Convoy which was delayed. I'm still waiting for it to arrive :/

Finally, is there some limit of value of an order when customs charges extra tax or similar?
The limit including postage is $1000AUD. Over that amount you get charged tax for the total including shipping cost.